Natural frequency is one of the parameters that represent useful information about the dynamic behavior of structures. Controlling this parameter can decrease the probability of damage under dynamic loading. Weight optimization on layout and sizing with frequency constraints is a well known problem because of its highly non-linear behavior. Improved ray optimization (IRO) algorithm is utilized to solve truss layout and sizing optimization with multiple natural frequency constraints. This is a multi-agent algorithm and each agent is modeled as a ray of light with a location and direction. At each iteration, each light ray approaches a point which is defined based on the historically best position of the entire agents and the historically best positions of one agent to find the global or near-global optimum solution. To verify the efficiency of the IRO, five well-known benchmark problems are studied and their results illustrate the ability of the proposed algorithm in finding the optimal solution.